DC/DC chargers, How do they work and do you really need one.

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Originally Posted by Silenceisgolden

Sorry Old Farang, when you wrote "It is not surprising that confusion arises! Exactly WTF are they trying to say here:" I thought you were asking a question.

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No problem.[thumbsupbig] Maybe whomever wrote it is not a native English speaker.

The OP asked; " in layman's terms" about what DC-DC conversion is. The simple answer is that you cannot use a magnetic type transformer to step up OR down a DC voltage, it only works with AC. Back in the days of sailing ships when I started the most common way to convert DC voltage was to use a "rotary converter". Some were motor driven "generators", either AC or DC motors, direct coupled or belt driven, or if you were REALLY posh, a self contained motor / generator.

Then all you young blokes got in on the act and developed electronic versions. So basically; DC input is taken, converted to AC internally just like a DC inverter, adjusted up or down depending on what is required, then converted back to DC output. And don't be fooled by any claims of 100% efficiency, it is not possible.

Whether you need one or not I will leave up to those that know!

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Originally Posted by Tombie

In line infers series which is not the case if they are 12v batteries, they are in parallel which provides 12v.

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Yes thats what i meant to say [thumbsupbig]

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Originally Posted by Silenceisgolden

Hint - google "causes of diode failure in alternators".

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Another hint,it could have been Professor Plum,in the kitchen, with the candlestick[bighmmm]

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Originally Posted by Old Farang

Back in the days of sailing ships when I started the most common way to convert DC voltage was to use a "rotary converter". Some were motor driven "generators", either AC or DC motors, direct coupled or belt driven, or if you were REALLY posh, a self contained motor / generator.

Then all you young blokes got in on the act and developed electronic versions. So basically; DC input is taken, converted to AC internally just like a DC inverter, adjusted up or down depending on what is required, then converted back to DC output.

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Yep, they were also called genemotors, esp. in WW2. And I am an old fart, not a young bloke. I made my first 'electronic version' transistorised DC-DC converter 45 years ago, so I could run a 12 volt system on my 6 volt BSA C10 side valve motorbike without going to the expense of having the generator rewound.

As a marine sparky way back I did come across burned out alternators I guess "modern" vehicles have alternators that can handle it all but have a look at this:

YouTube

It is not impossible to burn up an alternator I guess?

Back to the DC/DC story, it has been explained relatively well all in all I think so I will refrain from adding more at this point. I did write this pages long answer yesterday but had to step out and when I clicked post when I came back, that bloody irritating auto logout had kicked in and after logging back in it was all gone so, yeah.

Having said that, I have my 12V system on the testbench for a few months now and I have made a lot of test measurements. I might take the time and effort to document it for others to have a look at seeing as more people seem to be interested in it.

Cheers,
-P

Hi prelude, it is misleading garbage like that video that makes it near impossible to get legitimate info on to the internet.

There is one single factor omitted from the test, that is the reason that alternator burnt out.

if you were running your alternator at full current capacity, you would most likely be driving at at least 80+ KPH.

At that sort of speed, there would be a HUGE flow of air passing around and through your alternator.

They have not got so much as a fan on that alternator. That is nothing more than an engineered bogus demonstration.

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There is one single factor omitted from the test, that is the reason that alternator burnt out.

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I watched that vid despite the bloody annoying commentary and they Did give a reason, They did state that the alternator was spinning too slow to be able to cool itself down via the internal fan while still pumping out the high amps needed .
It is a pretty good example of why you need specialised battery management when charging Lithium batteries.

Yes, they overlook the fact that car alternators run at least 3 times, some of them more, than the engine speed. I think that their object was to show what can happen charging different types of batteries.

Sorry folks, it's a con job.

You have heaps of people already using lithium cranking batteries and they don't burn out alternators.

This is nothing more than dishonest sales hype.

[QUOTE=trout1105;3000632]My understanding as a "Layman" abut these units is that with modern (Post 2006) 4WD's the alternator doesn't put out enough voltage to keep the Deep Cell batteries at 100% SOC and the DC/DC chargers can increase that voltage to get the secondary battery/batteries up to 100%SOC........................

What's SOC mean? - please excuse my ignorance
cheers Gerald